Floyd's Triangle Program in Java

What is Floyd's Triangle

Floyd's Triangle is a right-angled triangle of numbers, filled row by row with numbers counting up continuously. Row 1 has one number, row 2 has two, and so on. It is a classic pattern exercise combining nested loops with a running counter.

The pattern

For 4 rows, Floyd's Triangle looks like:

1
2 3
4 5 6
7 8 9 10

Notice the numbers never restart — they flow continuously. Row 3 ends at 6, so row 4 begins at 7. Each row has one more number than the last.

The Java program

public class Floyd {
    public static void main(String[] args) {
        int rows = 4;
        int num = 1;                 // running counter

        for (int i = 1; i <= rows; i++) {
            for (int j = 1; j <= i; j++) {
                System.out.print(num + " ");
                num++;               // never resets
            }
            System.out.println();    // new line per row
        }
    }
}

The outer loop i is the row; the inner loop runs i times to print that row's numbers. The key is num, which keeps counting up and is never reset.

Dry run

The running counter

The heart of Floyd's Triangle is that num is declared before the loops and increased after every print, but never reset inside a row. This continuous counting is what makes the numbers flow smoothly from one row to the next, unlike patterns that restart each row.

Common mistakes

• Resetting the counter each row. Declare num outside the loops so it keeps rising.
• Wrong inner loop limit. Row i needs j <= i to print i numbers.
• Forgetting the newline. Add println() after each row.
• Confusing rows and counter. Rows control how many numbers; the counter controls their value.

Summary

• Floyd's Triangle fills numbers row by row, continuously.
• Row i has i numbers.
• Use nested loops: outer for rows, inner for numbers.
• Keep a single counter that never resets between rows.
• Add a newline after each row.

Next, try more shapes in nested loops, or a maths pattern in the Armstrong number program.